It has been conventionally known a coordinate calculation method to calculate sight line detection coordinates that indicate a position of user's sight line on a display screen image based on an output signal outputted from a sight line detection device that detects a direction of user's sight line, to calculate a value of manual input correction based on information of user's manual input operation received from an operation device such as a mouse, and to obtain input coordinates by adding the value of manual input correction to the sight line detection coordinates (for example, see patent literature 1).